The present invention concerns a former head with needle rollers of the kind used in dry formation of fibrous tissue, where a fibre material is supplied to the former head mixed with air via one or more injection nozzles.
From the industry there are known former heads where at the ends of rotating perforated cylinders a mixture of fibres and air is injected. Within the cylinders, a needle roller, also rotatable, is suspended and keeps the individual fibres afloat so that clotting does not occur before the fibres are sucked with vacuum through the perforation in the cylinder and are fixed on an underlying former wire.
From U.S. Pat. No. 3,252,186 is furthermore known a former head with needle rollers co-operating in pairs, where the rotational speed of the rollers are different in a ratio up to 1:3, i.e. one rotates at e.g. 900 rpm, whereas the other rotates at 2700 rpm. Allegedly, a kind of impact crusher effect separating the fibres is here achieved. The technique according to U.S. Pat. No. 3,252,186, however, has the drawback that the fibre distribution does not become very good, as the fibres are released from the roller set over a relatively small length in the longitudinal direction of the underlying former wire. A variant of the art according to U.S. Pat. No. 3,252,186, may comprise two sets of needle rollers or beater rollers acting in pairs and with variable overlap. These two sets are, however, placed immediately above each other, which does not give an improved distribution of the fibres. The fibre supply to this former head occurs by means of conveyor belts from which fibres are sprinkled down between the two co-operating rollers. Alternatively, air nozzles may be mounted, supplying air to the area between the rollers in order thereby to improve the distribution quality of the fibres.
With a former head according to the invention it has been realised that a markedly improved capacity and distribution quality of fibre may be attained, where the length is about 2 mm or more compared with a product formed in traditional former heads.